This proposal deals with roles for arachidonic acid epoxygenases in regulating functions of epidermal keratinocytes. The cytochrome P450 CYP2B19 generates 14,15- and 11,12-epoxyeicosatrienoic (EET) acids from arachidonate. CYP2B19-expressing granular keratinocytes comprise the outermost, viable, cell layer of the epidermis, where the epidermal, water permeability barrier forms. Functions of these cells largely determine our ability to respond to, and recover from, hostile environments and injury. In the previous grant, we showed that 14,15-EET promotes keratinocyte comification, by mechanisms involving transglutaminase activation. Transglutaminase activities are essential for the transition of granular cells to squames (anucleated, comified cells) and for a competent epidermal barrier. We hypothesize that EETs are involved in controlling functions of terminally differentiated skin keratinocytes in vivo, that this regulation ultimately specifies epidermal barrier properties and, as consequence, ability to respond to and recover from harmful environmental stress and injury. This proposal investigates mechanisms how EETs exert their biological effects on keratinocytes in vitro and the effects of EETs on epidermal barrier function in vivo. Aim 1 would prove whether P450-dependent metabolic activation or peroxisome proliferator-activated receptor (PPAR)a are involved in mediating 14,15-EET effects on keratinocytes cornification. Aim 2 would prove whether CYP2B19 metabolites regulate transepidermal water loss or ceramide content, during repair of the barrier after tape stripping mouse skin. Finally, Aim 3 would prove the fundamental role of P450 epoxygenases in the epidermis by generating Cyp2b19 null mice and studying effects of loss of function on (a) ability of epidermal keratinocytes to differentiate and (b) competency of epidermal barrier functions in intact animals. Stratified squamous epithelia like the epidermis directly interface and function as a barrier to the environment; as such they are primary sites of disease and cancers. We propose to study how endogenously formed lipid mediators (EETs) regulate organ function. These studies are important to human health since defects in the epidermal barrier increase susceptibility to toxicities, physical injuries, infections, and even death by water loss. [unreadable] [unreadable] [unreadable] [unreadable] [unreadable]